In general, diesel engine vehicles run on gas fuel. Recently, the following problem has become a matter of public concern. That is, emissions, such as NOx, unburned hydrocarbons, and particles, contained in exhaust gas cause air pollution to impair human health.
Therefore, various techniques have been developed to clean exhaust gas from diesel engines. The amount of emitted NOx and particulates are reduced with, for example, ceramic filters or special catalyst devices attached to ends of exhaust pipes of engines.
Diesel engine vehicles, particularly heavy-duty trucks, have a large piston displacement and therefore emit a large amount of exhaust gas from their engines. Hence, exhaust gas-cleaning systems for these vehicles are large in size. Furthermore, since chemical substances contained in the exhaust gas are trapped with micropore filters or catalysts, an increase in mileage causes clogging. Therefore, internals of the systems must be cleaned at periodic intervals, whereby clogging materials are removed.
In recent years, in order to avoid the increase in the system size and in order to eliminate cleaning operations, some techniques for reducing the amount of particles in exhaust gas by improving diesel fuel have been developed.
One of such techniques includes a proposal of an apparatus for preparing emulsion by mixing water and diesel fuel such as gas oil and then agitating the liquid mixture with a screw propeller. An emulsion fuel prepared in such a manner can be completely burned because water is vaporized by combustion to create a small explosion. Thus, the amount of created NOx and particles is slight.
For such a screw-type agitating unit, there are problems in that the size thereof is large and it takes a long time to prepare the emulsion fuel. Furthermore, for the emulsion fuel, there is a problem in that water and oil are separated from each other in a short time while the emulsion fuel is allowed to stand for a while because water clusters contained in the emulsion fuel have a large size.
Various liquid mixtures are used to produce, for example, industrial materials such as ceramic materials, paste food products such as creams, cosmetic products or drug products in addition to fuel products. Such liquid mixtures for these uses must have properties required for preparing intermediate or final products, having high accuracy in size and shape and high quality, for industrial uses, properties required for preparing food having good eating quality, superior cosmetic properties, or high drug properties. In these uses, any liquid mixture with an ultra fine particle size and high mixture density has not been obtained.
Japanese Unexamined Patent Laid-open Publication No. HEI 10-277375 discloses a known technique for converting fuel into emulsion having a fine particle size using adiabatic expansion and ultrasonic waves. For this technique, the emulsion is uniform because cavitation is not used.
Japanese Unexamined Patent Laid-open Publication No. HEI 8-310971 discloses a known technique for achieving a high contrast effect with a small dose of a contrast medium for ultrasonic diagnosis by promoting the vaporization of a dispersant using ultrasonic cavitation.
Furthermore, Japanese Unexamined Patent Laid-open Publication No. HEI 10-298051 discloses a known technique for preparing an oil-in-water emulsion with good stability by mixing oil and water together with polymer particles and then homogenizing the mixture using cavitation.
For the known technique for mixing fuel such as gas oil with an incompatible liquid such as water to prepare an emulsion fuel, there are problems in that the apparatus is large in size because of the location of a screw-type agitating unit, it takes a long time to prepare the emulsion fuel, and water and oil in the emulsion fuel are separated from each other in a short time, as described above. Therefore, this technique cannot be directly applied to diesel engines and combustion units such as boilers.
According to the technique described in Japanese Unexamined Patent Laid-open Publication No. HEI 10-277375, in order to prepare uniform emulsion by finely atomizing the fuel using adiabatic expansion and ultrasonic waves, it is preferable not to generate cavitation. This theory is based on the fluidity of the fuel finely atomized. In order to finely atomize liquid, it is considered to be preferable to use high energy due to cavitation effect, as described in the known documents (Japanese Unexamined Patent Laid-open Publication Nos. HEI 8-310971 and HEI 10-298051).
However, neither any system nor any method of efficiently achieving high energy is particularly disclosed in the above two documents relating to the utilization of cavitation effects. Examples of an ordinary technique for achieving such cavitation effects include an agitating unit, as well as the screw-type agitating unit, operated in liquid at high speed and a single vibrating plate vibrating in liquid at high speed. However, any sufficient cavitation effect cannot be necessarily achieved and any liquid mixture with a fine particle size can hardly be prepared efficiently utilizing such a technique. For a liquid mixture prepared by utilizing any one of the known techniques, there is a problem in that the quality of the mixture cannot be maintained for a long time because liquid components are readily separated from each other in a relatively short time as described above.
Any liquid mixtures for producing industrial materials such as ceramics, paste food products such as creams, cosmetic products, and drug products having an ultra fine particle size and high mixture density cannot be necessarily obtained by the known techniques, which cannot sufficiently cope with requirements such as an improvement in quality.
Examples of a liquid mixture include a mixture prepared by mixing liquid components, a mixture prepared by mixing a liquid component and a gas component, a mixture prepared by mixing a liquid component and a power component, and a mixture prepared by mixing some of these mixtures. These mixtures prepared by the known techniques do not necessarily have an ultra fine particle size.
The present invention has been made to solve the above problems. It is an object of the present invention to provide techniques for extremely efficiently generating cavitation to produce various liquid mixtures having an ultra fine particle size using the cavitation. In particular, it is an object of the present invention to provide an apparatus for mixing liquids and a method of mixing such liquids. The apparatus and method are useful in producing a liquid mixture, such as an emulsion fuel, an industrial liquid material, a food product, a cosmetic product or a drug product, having a ultra fine particle size, high mixture density and high quality in a short time with high efficiency. Liquid components of the liquid mixture are hardly separated from each other even if the liquid mixture is stored for a long time.